Solo TK

No, doubt you'll be able to do Kael'Thas due to his mechanics. (one of them being mind controlling people) But then again I doubt you'd get to that phase to begin with
P1 should be np, p2, yea should be doable, p3 should mean you die, p4 should also get you killed and well, same with p5.

Raegwyn did it by pulling a few of the bosses all the way back to the entrance of the instance though. I'm not certain if this is still possible, or if Blizz has since put locking doors in Kael's room.

You're certainly welcome to try, but it may be impossible or at least significantly more difficult if Blizzard has patched that little hole.

I solod him on my 90 hunter, 90 ele shaman, and 90 dk, the key to the solo is p3, when killing the 4 npcs in p1 kill them each in the 4 corners of the room then when p3 starts stand near the mage nuke her then, i killed the engineer, then warrior then it was pretty simple